feat: 階段一 - 改用 Node.js 實作基本流程骨架

- Dockerfile: 改用 node:20-slim
- entrypoint.sh: 執行 app/main.js
- app/package.json: axios + js-yaml + openai
- app/config.js: 環境變數與 LLM 自動偵測（10 種服務）
- app/llm.js: OpenAI-compatible 統一介面
- app/gitea.js: PR diff 取得與 comment 發布
- app/roles.js: 從 prompts/roles/*.yaml 載入角色
- app/main.js: pipeline 骨架，log 每個主要階段

app/main.js

@@ -0,0 +1,71 @@
+import { GITEA_REPOSITORY, PR_NUMBER, PR_HEAD_BRANCH, PR_BASE_BRANCH, getLLMConfig } from './config.js';
+import { loadRoles, getRoleIntro } from './roles.js';
+import { getPRDiff, postComment } from './gitea.js';
+
+async function main() {
+  console.log('='.repeat(60));
+  console.log('🚀 Step1: Pipeline 啟動');
+  console.log(`  repo=${GITEA_REPOSITORY}  PR=#${PR_NUMBER}`);
+  console.log(`  ${PR_HEAD_BRANCH} -> ${PR_BASE_BRANCH}`);
+
+  // 偵測 LLM
+  const { provider, baseURL, model } = getLLMConfig();
+  if (!provider) {
+    console.error('❌ 未設定任何 LLM API Key，請檢查 action inputs');
+    process.exit(1);
+  }
+  console.log(`  LLM: provider=${provider}  model=${model}  base_url=${baseURL}`);
+
+  // 載入角色
+  const roles = loadRoles();
+  console.log(`  已載入 ${roles.length} 個角色: [${roles.map(r => r.name).join(', ')}]`);
+
+  // 取得 PR diff
+  console.log('\n📋 Step1: 取得 PR Diff');
+  let diff;
+  try {
+    diff = await getPRDiff();
+    console.log(`  diff 長度: ${diff.length} 字元`);
+  } catch (e) {
+    console.error(`  ❌ 取得 diff 失敗: ${e.message}`);
+    process.exit(1);
+  }
+
+  if (!diff.trim()) {
+    console.log('  ⚠️  diff 為空，無需審查');
+    process.exit(0);
+  }
+
+  // 發布角色介紹 comment
+  console.log('\n💬 Step1: 發布角色介紹 Comment');
+  try {
+    const intro = getRoleIntro(roles) + `\n\n> 🔍 服務：${provider}  模型：${model}`;
+    await postComment(intro);
+    console.log('  ✅ 角色介紹 comment 發布成功');
+  } catch (e) {
+    console.log(`  ⚠️  comment 發布失敗（繼續執行）: ${e.message}`);
+  }
+
+  console.log('\n📊 Step2: Findings 產生（待實作）');
+  console.log('  [stub] 各角色分析 diff...');
+
+  console.log('\n🔀 Step3: Findings 合併與去重（待實作）');
+  console.log('  [stub] 合併新舊 findings...');
+
+  console.log('\n📝 Step4: Findings 寫入與 Comment 發布（待實作）');
+  console.log('  [stub] 寫入 findings.json，發布 comment...');
+
+  console.log('\n💾 Step5: 記憶區 Commit/Push（待實作）');
+  console.log('  [stub] commit & push findings.json...');
+
+  console.log('\n🚦 Step6: 嚴重問題檢查（待實作）');
+  console.log('  [stub] 檢查 critical findings...');
+
+  console.log('\n✅ Pipeline 完成');
+  console.log('='.repeat(60));
+}
+
+main().catch(e => {
+  console.error('❌ Runner failed:', e.message);
+  process.exit(1);
+});